Coupled granular/continuous (CGC) perpendicular media increases thermal stability without compromising SNR. However, increasing thermal stability by using a continuous layer leads to concerns regarding transition noise. Investigating these concerns, we examine bit transition irregularity in CGC media using a 3D micromagnetic model with sub-grain discretization. Irregularity is introduced by writing tracks diagonally to the x-y axes of the cubic computational cell. Initially we model the granular layer as ideal, with exchange decoupled grains. The investigation is then extended to a nonideal system by varying intergranular exchange coupling in a system of comprising clusters of 10 nm grains. The thickness of the granular layer, g, and the continuous layer, c, are varied while maintaining a constant media thickness. For a range of thickness ratio, R(=c/g), that depends on intergranular exchange coupling in the granular layer, it is found that bit transition irregularity is reduced to less than that of the underlying granular physical structure. In CGC media with 50 nm grains, the irregularity is reduced to that of a granular media with ≈10 nm grains. Thus, in addition to enhancing thermal stability, CGC media may provide a way to reduce noise, thereby extending the limit to the areal density of conventional media.
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